1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device.
2. Description of the Related Art
Conventionally, there has been known a semiconductor device where noises generated by high-speed switching (for example, radio noises) can be decreased (see JP-A-2011-134984 (patent literature 1, for example).
FIG. 20A to FIG. 20C are views for explaining a conventional semiconductor device 900. FIG. 20A is a plan view of the semiconductor device 900, FIG. 20B is a cross-sectional view taken along a line x-x in FIG. 20A, and FIG. 20C is an enlarged view of an essential part of a region surrounded by a broken line A in FIG. 20A. In FIG. 20A to FIG. 20C, symbol 926 indicates an interlayer insulation layer, and symbol 928 indicates a source electrode layer. In FIG. 20A and FIG. 20C, the interlayer insulation layer 926 and the source electrode layer 928 are not shown.
The conventional semiconductor device 900 is, as shown in FIG. 20A to FIG. 20C, a MOSFET which includes: a cell region which is defined on a semiconductor substrate on which an n+ type low-resistance semiconductor layer (not shown in the drawing) and an n− type drift layer 914 are laminated; and a peripheral region which includes a gate finger forming region which surrounds the cell region and a gate pad forming region which projects into the cell region.
The semiconductor device 900 includes, in the cell region: the low resistance semiconductor layer; the n− type drift layer 914 formed over the low resistance semiconductor layer; a p-type base region 916 formed over a surface of the drift layer 914; an n-type high-concentration semiconductor region 920 formed over a surface of the base region 916; a gate electrode layer made of polysilicon and formed over the base region 916 sandwiched between the drift layer 914 and the high-concentration semiconductor region 920 by way of a gate insulation layer 922. The semiconductor device 900 includes a plurality of gate electrode layers 924 formed in a stripe shape as the gate electrode layer.
The semiconductor device 900 includes, in the peripheral region: the low resistance semiconductor layer (not shown in the drawing); the drift layer 914 formed over the low resistance semiconductor layer; gate lead lines (not shown in the drawing) made of polysilicon, formed over the drift layer 914 by way of a field oxide film (not shown in the drawing), and formed in a gate finger forming region and a gate pad forming region; a gate finger 940 made of metal and formed over the gate lead lines in the gate finger forming region; and a gate pad 942 made of metal, formed over the gate lead lines in the gate pad forming region, and connected to the gate finger 940.
In the semiconductor device 900, the gate electrode layers 924 and the gate lead lines are electrically connected to each other by way of a resistor 944 made of polysilicon containing an impurity. An impurity concentration in polysilicon which forms the resistor 944 is equal to an impurity concentration in polysilicon which forms the gate electrode layers 924, and a width of the resistor 944 is narrower than a width of the gate electrode layer 924. Since the width of the resistor 944 is narrower than the width of the gate electrode layer 924, an internal resistance of the resistor 944 becomes higher than an internal resistance of the gate electrode 924.
According to the conventional semiconductor device 900, the gate electrode layers 924 and the gate finger 940 are electrically connected to each other by way of the resistors 944 and hence, a falling of an electric current at the time of turning off the semiconductor device 900 can be made gentle by increasing a charge/discharge time constant of the gate. Accordingly, dv/dt at an overshoot portion of a voltage becomes small at the time of turning off the semiconductor device 900 whereby noises generated due to high-speed switching can be decreased.